Electric Current through the Atmosphere

"The conduction current is the largest portion of
the air-earth current, far outweighing the contributions made by the precipitation
current and convection current, which are zero in storm-free regions. Its
magnitude is approximately 3 × 10-12 amperes (A) m-2, or about 1800
for the entire earth."

"Its magnitude is approximately 3.5E-12 amp/m2, quite
a feeble current density, which however for an earth mean radius of
6371.3 km, works out to be about 1800!! amperes for the entire earth."

1800 A

Have you ever witnessed an unusual incidence where an unplugged electrical
appliance turned on? Or have you seen sparks come off ungrounded metal
wires? The reason
for these strange event may lie within the atmosphere. Yes, you heard correctly
-- the atmosphere! It is the largest source of naturally produced electricity
on earth. Several generators of this electricity are cosmic rays, thunderstorms,
lightning and static electricity. The most interesting of these are thunderstorms
and lightning. The earth can be considered as a big battery, and thunderstorms
pump back electrons that the earth gives off. It is estimated that without
that replenishment of electrons, the earth would lose all of its charge
within an hour.

There are about 2,000 to 6,000 thunderstorms any given moment, which means about
100 lightning bolts per second. This translates to about 300,000 to 400,000
V between the earth and the ionosphere (the part of the atmosphere that can
be ionized). Electron flow does not cease to exist in fair weather conditions
between the earth and atmosphere. Fair weather condition is defined as any
time when it is not rainy or stormy. The amount of electricity within the atmosphere
at that time has been calculated to be between 1000 and 1800 A, with 1800 A
being the most commonly accepted value.

The fair weather current flow occurs as follows: positive ions flow to the earth
and negative ions flow to the ionosphere. Thus, positive charges deposit on
Earth and negative charges deposit in the ionosphere. This flow depletes the
extra electrons on Earth and the difference of charge allows the flow to cycle.
Now you may ask why we all aren't being electrocuted while on Earth' surface.
This is because the current is spread out over the whole of the earth; we won't
feel it because it is distributed over a large area. This means about 3.5 microamps
per square kilometer (9 microamps per square mile) or about 260 V between the feet and the head of a 1.8 meter tall (6 foot) person.